1. Field of the Invention
The present invention relates to a recording liquid suitable for ink-jet recording which employs a metallized azo red pigment.
2. Description of the Related Art
Ink-jet recording is rapidly gaining acceptance by the public as a recording process because it generates little noise and permits economical multicolor printing.
The ink-jet recording process is a process for performing recording on a recording element or medium in which droplets of a recording liquid (i.e., an ink) are ejected or propelled from a print head having one or more orifices onto the recording element.
In ink-jet recording, numerous schemes are utilized to control the deposition of the ink droplets onto the image-recording element to yield the desired image. In one process, known as continuous ink-jet recording, a continuous stream of droplets is charged and deflected in an image-wise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink-jet recording, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation.
The recording elements used in such recording processes typically comprise the so-called "plain papers," and, for higher image quality applications, an ink-receiving or ink-receptive layer provided on a support. The recording elements include those which are intended for reflection viewing, which usually have an opaque support, and those which are intended for viewing by transmitted light, which usually have a transparent or translucent support.
The ink compositions used to image the image-recording elements employed in such recording processes are typically liquid compositions comprising a solvent or a carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives, and the like. The solvent or carrier liquid can be predominantly water, although ink compositions in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid also are used. The dyes used in such compositions are typically water-soluble direct or acid type dyes.
When metallized azo red pigments such as Pigment Red 57 and Pigment Red 52 are employed as coloring agents in water-based ink compositions, i.e., ink compositions which consist predominantly of water as a carrier fluid, it has been found that the ink compositions rapidly increase in viscosity, thicken and eventually gel rendering them useless for ink-jet applications. Thus, it would be highly desirable to provide, as ink compositions suitable for use in ink-jet printing processes, pigment dispersions or suspensions of metallized azo red pigments such as Pigment Red 57 and Pigment Red 52 in water, which are stable and fluid for extended periods of time and in which the pigment particles resist settling. The present invention provides such ink compositions by including in the compositions, as a sequestering agent to prevent the compositions from thickening and/or gelling, an alkali metal, an alkaline earth metal or an ammonium salt of a linear aliphatic substituted glycine.